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docs(audit): VirtualTags.md — correct write-reject mechanism (review fix)

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Joseph Doherty
2026-06-03 15:51:15 -04:00
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docs/VirtualTags.md
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@@ -103,7 +103,7 @@ Per [ADR-002](v2/implementation/adr-002-driver-vs-virtual-dispatch.md) Option B,
- `ReadAsync` fans each path through `engine.Read(...)`.
- `SubscribeAsync` calls `engine.Subscribe` per path and forwards each engine observer callback as an `OnDataChange` event; emits an initial-data callback per OPC UA convention.
- `UnsubscribeAsync` disposes every per-path engine subscription it holds.
- **`IWritable` is deliberately not implemented.** `GenericDriverNodeManager` rejects OPC UA client writes to virtual nodes with `BadUserAccessDenied` before any dispatch — scripts are the only write path via `ctx.SetVirtualTag`.
- **`IWritable` is deliberately not implemented.** Virtual-tag nodes are not client-writable because `OtOpcUaNodeManager.EnsureVariable` materialises every SDK variable with `AccessLevel = AccessLevels.CurrentRead`; the SDK base `CustomNodeManager2.Write` returns `BadNotWritable` for read-only nodes and v2 has no client-write dispatch path. Scripts are the only write path via `ctx.SetVirtualTag`.
`NodeSourceKind` on each `DriverAttributeInfo` (set by `EquipmentNodeWalker` at address-space build time) drives which backend handles a read. See [ReadWriteOperations.md](ReadWriteOperations.md) and [v1/Subscriptions.md](v1/Subscriptions.md) for the broader dispatch framing.